What are the correct heads for 2006 Mercruiser 5.0 MPI?

juhasev

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I bought my boats with 45 hours on it and at 350 hours I have two cracked heads and water in the oil (cracked in exhaust valve seats). After inspecting the heads they don't appear to be marine heads which to my knowledge should always have steel re-enforced valve seats. Also the combustion chamber appears to be a slightly larger than in the marine heads potentially leading into HP loss. So my question is what is the correct head? Did Mercruiser sell heads without the steel re-enforced valve seats or did somebody at some point replace my boats engines and cheap skated putting in wrong heads?

I have attached picture of my heads and Sierra Vortec cylinder head with steel reinforced valve seats (see the difference in combustion chamber)

Has anybody used Sierra heads? I would assume they would work as good as the Mercruiser equivalents. After all they are probably all using the same casting....

Any help would be appreciated!

Thanks, Juha
 

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Bondo

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I bought my boats with 45 hours on it and at 350 hours I have two cracked heads and water in the oil (cracked in exhaust valve seats). After inspecting the heads they don't appear to be marine heads which to my knowledge should always have steel re-enforced valve seats. Also the combustion chamber appears to be a slightly larger than in the marine heads potentially leading into HP loss. So my question is what is the correct head? Did Mercruiser sell heads without the steel re-enforced valve seats or did somebody at some point replace my boats engines and cheap skated putting in wrong heads?

I have attached picture of my heads and Sierra Vortec cylinder head with steel reinforced valve seats (see the difference in combustion chamber)

Has anybody used Sierra heads? I would assume they would work as good as the Mercruiser equivalents. After all they are probably all using the same casting....

Any help would be appreciated!

Thanks, Juha

Ayuh,.... Welcome Aboard,.... Donno what you've got goin' on there, but the picture is of a Pre-vortec head,.....

How many bolts hold the intake manifold,..?? should be only 8,....

For the 350, there's two castin' numbers, 906, 'n 662,....
906 is possibly the Better of the 2, because of hardened valve seats, over induction hardened seats,...

I ain't sure of the 305 Vortec heads, as 350 heads can shroud the valves when used on the 305,...

Btw,... Yer abit confused on the Marine differences,....
Mercuiser used Chevy long blocks, pretty much exactly like Chevy's pickup motors for any given year,...
That Includes the heads,...
Nothin' Special 'bout Marine heads, atleast for our standard marine production motors,...
 

Scott Danforth

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305 vortec heads have smaller valves than the 350.

as Bondo said, nothing special about the heads. find a set of 1996-2002 305 V8 heads in a u-pull it salvage yard for $100, spend $200 to get them redone and bolt them on. or buy new heads complete for $400 each and bolt on
 

Scott Danforth

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regarding the casting number, the L30 vortec (305) casting number is 12558059 or 12552520 . 1.84" intake, 1.5" exhaust
 

juhasev

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Thanks for the info! So I am fine using the Vortec heads then? I don't want an another cracked valve seat for sure.... My question still remain should my 2006 Mercruiser 5.0 MPI have come Vortec heads in the first place? The machine shop told me that 12558059 is the correct casting number for my engine and that my engines should have come with those. I believe mine had casting number 12552520 on them.
 
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Scott Danforth

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either casting number will work 12558059 or 12552520. its the exact same head, however one came out of Tonawanda, and the other out of one of the Michigan powertrain plants
 

Bondo

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Thanks for the info! So I am fine using the Vortec heads then? I don't want an another cracked valve seat for sure.... My question still remain should my 2006 Mercruiser 5.0 MPI have come Vortec heads in the first place? The machine shop told me that 12558059 is the correct casting number for my engine and that my engines should have come with those. I believe mine had casting number 12552520 on them.

Ayuh,..... Yer not sayin' the 1st picture you posted is that head,..?? Are you,..??

The 1st picture posted is Not a Vortec head,...
 

juhasev

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Ok I think I am finally starting to understand this. So somebody attempting to sell me 5.7 heads as 5.0 heads. I've attached the picture with differences. Sierra heads listed as 5.0 heads are just listed with 5.7 picture, I will find out tomorrow.

Why doesn't the 5.0 engines come with hardened seats?

Has anybody used HQ heads in Marine application? They do make one with hardened seats.... which I certainly want to get.
 

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Scott Danforth

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all (or nearly all) cylinder heads after 1974 have hardened seats. it was required after lead was no longer used in fuel.
 

Bondo

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Ayuh,.... I just learned something in yer crankshaft coalition link,...

The 305 heads, Don't have the heart shape chamber of the other Vortec designs, but a very slightly modified D shape chamber,...
305_VORTEC_CHAMBER_CN_059.jpg


The 350 heads, won't run on a 305, without machine work is stated there as well,....
 

Tail_Gunner

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The marine ind does something's a bit different Intake's in general the mpi intakes use larger injector's...the 4.3 uses a single plane intake...and they have put 454 tbi's on 4.3's..5.7's. I am going to check on part number's (heads) on the 5.0/5.7...the 5.0 jumped to 260hp? quite quickly i would not be surprised to see they are the same..... Notice the timing on a efi model

Models5.0L5.0L EFI
Propshaft Horsepower22012401
Propshaft Kilowatts16411791
Displacement305 cid (5.0 l)
Maximum rpm @ WOT34400-4800 rpm
Idle rpm in NEUTRAL3650 rpm5600 rpm6
Oil Pressure @ 2000 rpm30-60 psi (207-414 kPa)
Min. Oil Pressure @ Idle4 psi (28 kPa)
Thermostat160o F (71o C)
Timing @ Idle rpm410o BTDC8o BTDC
Firing Order1-8-4-3-6-5-7-2
Electrical System12-Volt Negative (-) Ground
Alternator Rating ? Hot
Operating Amps
65 Amps
Alternator Rating ? Cold
Operating Amps
72 Amps
Recommended
Battery
Rating (Minimum)
375 cca/475
mca/90 Ah
550 cca/700
mca/120 Ah
 
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Tail_Gunner

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Well i cant edit that post so all this does not matter you have a efi engine and need to stay with the 059 heads as Scott pointed out..any flow improvement would need a new ecm calibration.
 

Fun Times

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Well i cant edit that post.
Hey Gunner, if you'd like to add some additional info to a post, please feel free to just post another post as a part two. If you need to remove the info due to wrong info or something of that nature, you are welcome to flag the post with a message of what you'd like done to the post or send one of us a private message. Sorry for the inconvenience of the missing edit...The system is on a one hour time set to edit.
 

Tail_Gunner

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Nothing new the op has efi and its of no use to Tinker as Don would say...It would cause more issue's than it's worth..Scott nailed it right on the head so to speak......:laugh:
 

juhasev

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Thanks everybody! I am going to go for 059 casting (305 heads)... or something similar maybe HQ or Sierra heads. So apparently there are 2 different methods of hardening the valve seats

1) Induction hardening
2) Steel rings.

The wikipedia article mentioned that the steel rings would be preferred for marine applications. Not sure if the steel rings are really that much better... All what I know that my heads cracked and they here not steel ring enforced and that most 5.7 heads come with the rings where as 5.0 usually don't.
 

Scott Danforth

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Remember, even you and I can edit Wikipedia, so take it as a grain of salt. Heads have had inductioned hardened seats since the 70's. Pre factory hardened heads can be modified with hardened seat inserts, however the labor and cost is only worth it on rare heads you are trying to salvage.... Like 409 or a 1929 Chord. The heads you are going to find for your 305 will have induction hardened seats.
 

Bondo

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Ayuh,..... Some time spent cruisin' 'round a Hot Rodder's forum can be enlightening,....
I sometimes go to the one of that name,....

As Scott says, most All heads, Chevy especially have had hardened valve seats since the '70s,.....
Some, probably most, induction hardened native iron,...
Others, cut, 'n pressed in hardened steel,...

One of the problems, as Yer seein' is,....
With modern castin' technologies, they're usin' less iron, so cracks happen Easier,...
An over-heat, from blocked water flow, lets the head go dry, it gets Hot, the pump picks up water, 'n quenches it with cold water, again, 'n again,....
It don't take as much of that, as the parts from years gone by,... more iron was used,...
 
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